As aqueous dispersion materials containing a functional substance have heretofore been well known, as functional materials, agricultural chemicals such as herbicides and insecticides, medicaments such as anti-cancer drugs, anti-allergic drugs and antiphlogistics, and coloring materials containing a colorant, such as inks and toners. In recent years, digital printing technology has been vigorously developed. Typical examples of this digital printing technology include those called electrophotographic technology and ink-jet technology, and its importance as image-forming technology in offices, homes and the like has increased more and more in recent years.
Among these, the ink-jet technology as a direct recording method has such a great feature that it is compact and low in consumed power. The formation of high-quality images is also quickly advanced by formation of micro-nozzles or the like. An example of the ink-jet technology includes a method wherein an ink fed from an ink tank is evaporated and bubbled by heating it by a heater in a nozzle, thereby ejecting the ink to form an image on a recording medium. Another example includes a method wherein an ink is ejected from a nozzle by causing a piezoelectric element to vibrate.
Since aqueous dye solutions are generally used as inks used in these ink-jet methods, in some cases, bleeding may occur when inks of different colors overlap with each other, or a phenomenon called feathering may appear in a direction of fibers in paper at a recorded portion on a recording medium. In order to improve these problems, U.S. Pat. No. 5,085,698 discloses the use of pigment-dispersed inks.
However, the ejection stability of an ink composition, among ink-jet recording properties, may not be sufficiently achieved in some case. A specific example includes a case where after an ink is ejected from a predetermined nozzle in an ink-jet recording head, the ink may be hard to stably re-eject when the ink is re-ejected from the nozzle after the ejection of the ink from the nozzle is suspended for a certain period of time. Besides, many other improvements are still desired under the circumstances.